A. Field of the Invention
The present invention relates to a conduit comprising 2 or more pipes that are twisted together. Said conduit is an integral part of a geothermal heating and cooling system. Geothermal heating and cooling systems are known for their superior performance in delivering efficient heating and cooling to homes, industrial buildings and residential and industrial complexes, as well as being environmentally clean and cost effective. See, for example,
http://www.igshpa.okstate.edu/geothermal/geothermal.html;
www.summitmechsystems.com/pages/3.1.html;
www.renewableheating101.com/geothermal/loops;
http://minnesotageothermalheatpumpassociation.com/geothermal/earth-loop-options/; and http://www.informedbuilding.com/Geothermal/Main16/Types-of-Geotherm. However, a barrier to the wide spread use of geothermal heating and cooling systems is the high cost of installation of the ground loop of pipes that the system requires. Also, the presently available ground-loop pipes are not ideal in terms of heat transfer and utilization of the borehole required to install the vertical ground loop pipes.
B. Description of the Related Art
The art has attempted to overcome these barriers to market entry for this efficient heating and cooling system. The aforementioned websites discuss the currently available ground loop technology. For example, the commonly used ground loop technologies are: horizontal ground loops, vertical ground loops, and slinky coil ground loops. However, horizontal ground loops require a substantial amount of land. Currently available vertical loops, including multiple pipe vertical loops use less land, but their configuration does not optimize heat transfer, as does the present invention. Finally, the slinky coil ground loop is a variation of the horizontal ground loop and it too requires a substantial amount of land.
Also, inventors have sought patents on conduits to solve the problems with the current technology. For example, U.S. Pat. No. 5,630,447 ('447) discloses a pipe design that utilizes the entire borehole; and therefore transfers more heat to the ground. Further, the '447 invention allows for reduction in the size of the borehole required for a pipe capable of handling a specified flow of heat transfer fluid. The '447 invention, however, has some limitations. Said limitation being the pipe design and the cost of said design both in terms of time and money. The standards set by ASTM specify that pressure pipes have a round configuration. The pressure rating is derived by a combination of material strength and diameter to pipe wall thickness ration. The smaller this ration the higher the pressure rating of the pipe will be. The pipe represented in U.S. Pat. No. 5,630,447 is not round according to the standard, set by ASTM, to determine pressure tolerance of a pipe, and therefore cannot be governed by the same standard. Thus, new standards will need to be written and approved by standard setting bodies such as ASTM and IGSHPA. This process could be costly and time consuming. Additionally the U.S. '447 pipe inherently keeps the heat transferring fluid in the in and out flow pipes in close proximity to each other; thus causing heat contamination from the inflow to the outflow pipe. U.S. Pat. No. 5,630,447 does address this problem by introducing the notion of an insulating space between the inflow and outflow pipe. However, this design further complicates the pipe design certification issues.
Finally, U.S. Pat. No. 5,477,914 ('914) discloses a ground source heat exchanger unit comprising a primary conduit and a plurality of secondary conduits for receiving heat transfer fluid. Said secondary conduits are spaced apart from each other. The '914 system is not designed for optimal use of the borehole due to the spacing between the secondary conduits. FIG. 1 of the '914 disclosure illustrates the fact that the '914 system requires greater land usage than a typical narrow borehole installation. Since the borehole is a very costly part of the installation of these systems, the '914 design becomes costly to install because of the larger diameter borehole required by the '914 system.
The '914 system will be inherently more cumbersome to manage because of the flexibility of the pipe in conjunction with the spacing required between the pipes. Specifically, it will be difficult to install the '914 invention in vertical boreholes and trenches because the pipes will tend to become disarranged from their designed arrangements. This is especially true when the installation takes place in a vertical borehole filled with water. The '914 inventor suggests a solution. He uses spacers installed at intervals on the pipe. However, this increases the cost of assembly and transportation of the '914 system.
Also, the '914 invention uses an insulated pipe. Said insulated pipe does not contribute to the heat transfer process while occupying space in the borehole, and system efficiency is compromised.
Vertical borehole installations of the ground loop are usually required to be at least partially grouted. To optimize heat transfer it is common to grout the entire bore. This is accomplished by the insertion of a grout pipe all the way to the bottom of the bore. This grout pipe can sometimes be very difficult to insert into the bore as it has a tendency to catch on various irregular surfaces. The added spacers in the '914 configuration in conjunction with the space between pipes will make inserting this grout pipe cumbersome and laborious because the pipe may get caught on the spacers.
Applicant's invention overcomes the problems with the art. Specifically, Applicant twists 2 or more pipes together, making more efficient use of the bore hole space by placing more pipe into the borehole; thus creating more heat transfer surface area than the presently available pipe configurations. The twisting of the pipes also improves heat transfer by increasing turbulent flow within the pipes.
Because the 2 or more pipes are twisted together, said twisted pipes will support one another during installation. Further, said twisted pipe arrangement is easily rolled up and transported to a job site.
Further, the grout pipe is an option, not a requirement. Said optional grout pipe may eliminate the need for insulating material to prevent cross contamination between in and out flow pipes when the pipe is evacuated of grout and replaced with air.
In sum, the advantages of the Applicant's invention over the current technologies are:
1. The conduit of the present invention can be manufactured from existing components and use in the market can begin almost immediately.
2. The conduit of the present invention allows for greater thermal transfer from pipe to ground. Not wishing to be bound by theory, the twisting of the 2 or more pipes improves heat transfer by increasing turbulence and increasing residence time in the in and out flow pipes. In other words, the present invention increases thermal transfer surface area due to the twisted pipe configuration; and turbulent flow in the twisted pipes increases heat transfer from pipe to ground. If desired, the optional grout pipe may be emptied of grout and replaced by air or any insulating gas, thus promoting pipe-to-pipe insulation.